Move WiiUtils to Core

Allows reusing the WAD import logic more easily, whereas UICommon
code can only be used from UICommon and UI.

And managing what's on the NAND is the Core's responsability, not UI.

Source/Core/Core/WiiUtils.h

@@ -0,0 +1,14 @@
+// Copyright 2017 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <string>
+
+// Small utility functions for common Wii related tasks.
+
+namespace WiiUtils
+{
+bool InstallWAD(const std::string& wad_path);
+}